With the increasing demand in multifunctional materials these days, when any material does not satisfy various desired properties, a material having higher performance may be manufactured by mixing different materials having superior properties.
It is typically exemplified by an insulation material comprising a metal-ceramic laminate. This insulation material compensates for low heat shield of a metal and brittleness of a ceramic by mixing a metal having mechanical rigidity with a ceramic having heat shield.
Examples of the composite may include a laminate composite by simply laminating two materials, a particulate composite by mixing two component particles in powder form, a fiber reinforced composite by implanting steel wires or fibers in a matrix in a specific direction, etc.
Especially, a laminate composite is mainly used for aircraft wings or insulation materials, and a composite made of concrete or by powder metallurgy is a typical example of a particulate composite. Also, a fiber reinforced composite may be utilized in rubber hoses, car tires, etc.
Recently, a laminate composite of two different materials is receiving attention as a novel material for lightweight constructions because the properties of materials for individual layers may be used together and thus superior mechanical properties such as high strength and hardness, superior wear resistance or superplasticity may be attained.
Meanwhile, thorough research into grain refinement is ongoing to improve the properties of materials all over the world. When a metal is subjected to plastic processing, a dislocation cell structure having small angle boundaries begins to form, and thus, in proportion to an increase in the amount of deformation, angle grain boundaries of dislocation cell subgrains increase and also grains become gradually refined. The method of applying a large amount of deformation to the metal using the above properties to thereby refine grains of the metal into ultrafine grains or nano-sized grains is referred to as a “rigid-plastic process,” which has recently increasingly become widespread.
In the rigid-plastic process, shear deformation, rather than compressive or tensile deformation, is more effective in terms of plastic deformation conditions which affect grain refinement of a metal. Hence, the shape of a mold has to be designed so that shear deformation may occur as much as possible in the rigid-plastic process. A variety of rigid-plastic processes, including ECAP (Equal Channel Angular Pressing), HPT (High-Pressure Torsion), ARB (Accumulative Roll Bonding), ECAR (Equal Channel Angular Rolling), etc., have been developed to date.